"Pattern Day Trader" Account Q's

I want to trade stocks. The problem is you cannot make more then 3 trades in 5 days? What is the definition of a trade thou. A round turn? If I buy 100 shares then 5 minutes later another 100.( Is it 2 trades already? ) Then I close half, (100 shares) and 5 minutes later close out the remaining 100, is that 4 trades?

Then there is something margin... 4-1 intraday and 2-1 overnight. What is this?